Method and apparatus for encoding motion information, and method and apparatus for decoding same

ABSTRACT

A method and apparatus for encoding and decoding motion information. The encoding method includes determining whether motion information of spatial prediction units that are spatially collocated to a current prediction unit and motion information of temporal prediction units that are temporally collocated to the current prediction are available; when the number of the motion information of the spatial prediction units and the motion information of the temporal prediction units is less than a predetermined number, generating additional candidate motion information by using the available motion information of the spatial prediction units and the motion information of the temporal prediction units such that the total number of pieces of candidate motion information is the predetermined number; and decoding motion information of the current prediction unit by using the ‘n’ pieces of motion information.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/129,813, filed Dec. 27, 2013, which is a national stage entry under35 U.S.C. §371(c) of International Patent Application No.PCT/KR2012/005091, filed Jun. 27, 2012, and claims the benefit of U.S.Provisional Patent Application No. 61/501,300, filed on Jun. 27, 2011,in the U.S. Patent and Trademark Office, the disclosures of which areincorporated herein in its entirety by reference.

BACKGROUND

1. Technical Field

One or more exemplary embodiments relates to a method and apparatus forencoding and decoding motion information, and more particularly, to amethod and apparatus for effectively encoding and decoding motioninformation of a current prediction unit.

2. Prior Art

Recently, as high definition video contents have become widely used, aneed for a video codec having a higher coding efficiency than aconventional video codec such as MPEG-4 H.264/MPEG-4 advanced videocoding (AVC) has increased.

According to motion compensation that is a technology for removingtemporal redundancy in a video signal, compression efficiency isincreased by transmitting a residual signal that is a difference valuebetween an original video signal and a reference signal indicated by amotion vector. In general, a motion vector and a residual value of eachblock, as an encoding result obtained by encoding each block by usingmotion compensation, are transmitted to a decoder. Since motion vectorsof each block occupy a considerable amount of an encoded bitstream,information about a motion vector assigned to each block needs to bereduced in order to increase compression efficiency.

In order to reduce transmission overhead during encoding of a motionvector, a motion vector of a previous block is used as a predictionmotion vector of a current block in a conventional MPEG-2 codec, and amedian of motion vectors of previously encoded blocks that are adjacentto a left side, an upper side, and an above-right side of a currentblock is used as a prediction motion vector of the current block in acodec such as MPEG-4 H.264/MPEG-4 AVC.

SUMMARY

One or more exemplary embodiment provides a method and apparatus foreffectively encoding and decoding motion information of a currentprediction unit.

According to one or more exemplary embodiment, various candidate motioninformation are generated by using motion information of predictionunits that are spatially collocated to a current prediction unit andmotion information of prediction units that are temporally collocated tothe current prediction unit.

According to one or more exemplary embodiment, compression efficiency ofan image may be increased by using various motion candidates obtainedbased on motion information of an adjacent prediction unit.

According to an aspect of one or more exemplary embodiments, there isprovided a method of encoding motion information including performingmotion prediction on a current prediction unit to obtain motioninformation about the current prediction unit; determining whethermotion information of spatial prediction units that are spatiallycollocated to a current prediction unit and motion information oftemporal prediction units that are temporally collocated to the currentprediction unit are available; as a result of the determining, when thenumber of the motion information of the spatial prediction units and themotion information of the temporal prediction units is less than apredetermined number ‘n’ (where n is an integer), generating additionalcandidate motion information by using the available motion informationof the spatial prediction units and the motion information of thetemporal prediction units such that the total number of pieces ofcandidate motion information is ‘n’; and encoding motion information ofthe current prediction unit by using the ‘n’ pieces of motioninformation.

The determining may include searching predetermined prediction unitspositioned above the current prediction unit in a predetermined scanningorder and selecting motion information of a first upper prediction unithaving available motion information as an upper spatial motioninformation candidate of the current prediction unit; searchingpredetermined prediction units positioned on the left of the currentprediction unit in a predetermined scanning order and selecting motioninformation of a first left prediction unit having available motioninformation as a left spatial motion information candidate of thecurrent prediction unit; and selecting motion information of aprediction unit of a previous picture selected from the previouspicture, based on a prediction unit of a previous picture having thesame location as the current prediction unit, as temporal motioninformation candidate of the current prediction unit, wherein thegenerating of the additional candidate motion information is performedwhen the total number of pieces of candidate motion information obtainedby using the upper spatial motion information candidate, the leftspatial motion information candidate, and the temporal motioninformation candidate is less than ‘n’.

The generating of the additional candidate motion information mayinclude generating motion information of an available upper predictionunit that is searched for after a first upper prediction unit havingavailable motion information is searched for, as the additionalcandidate motion information, in a predetermined scanning order.

The generating of the additional candidate motion information mayinclude generating the additional candidate motion information havingmotion information of an available left prediction unit that is searchedfor after a first left prediction unit having available motioninformation is searched for, in the predetermined scanning order.

The generating of the additional candidate motion information mayinclude scaling motion information of a prediction unit of a previouspicture having motion information from among remaining prediction unitsof the previous picture except for a prediction unit of a first previouspicture having available motion information and generating theadditional candidate motion information, when prediction units of aprevious picture, which is determined based on a prediction unit of aprevious picture having the same location as the current predictionunit, are scanned in a predetermined scanning order.

The determining may include selecting motion information ofpredetermined spatial prediction units of which locations are previouslydetermined from among predetermined prediction units positioned aboveand on the left of the current prediction unit, as a spatial motioninformation candidate of the current prediction unit; selecting motioninformation of a prediction unit of a previous picture selected from theprevious picture based on a prediction unit of a previous picture havingthe same location as the current prediction unit, as a temporal motioninformation candidate of the current prediction unit, wherein thegenerating of the additional candidate motion information is performedwhen a total number of pieces of candidate motion information obtainedby using the spatial motion information candidate and the temporalmotion information candidate is less than ‘n’.

The generating of the additional candidate motion information mayinclude generating predetermined motion information that is previouslydetermined, as the additional candidate motion information. Thepredetermined motion information may be motion vector having apredetermined value, a reference picture index having a predeterminedvalue, and reference direction information according to a slice type towhich a current prediction belongs.

The generating of the additional candidate motion information mayinclude, when motion information of the available spatial predictionunits and temporal prediction units includes bi-directional motionvector information of prediction of a direction L0 and a direction L1,generating the additional candidate motion information by adding andsubtracting a predetermined offset to and from a motion vector of theprediction of the direction L0 and a motion vector of the prediction ofthe direction L1.

When a first reference picture used in the prediction of the directionL0 and a second reference picture used in the prediction of thedirection L1 are positioned on the same location based on a currentpicture including the current prediction unit, the offset may be addedto the motion vector of the prediction of the direction L0 and themotion vector of the prediction of the direction L1, and when thecurrent picture is positioned between the first reference picture usedin the prediction of the direction L0 and the second reference pictureused in the prediction of the direction L1, the offset may be added tothe motion vector of the prediction of the direction L0 and a valueobtained by multiplying the offset by −1 is added to the motion vectorof the prediction of the direction L1.

The generating of the additional candidate motion information mayinclude changing prediction directions of motion information of theavailable spatial prediction units and motion information of theavailable temporal prediction units to generate the additional candidatemotion information.

The generating of the additional candidate motion information mayinclude, when the motion information of the available spatial predictionunits and the motion information of the available temporal predictionunits include bi-directional motion vector information of the predictionunit of the direction L0 and the prediction unit of the direction L1,generating the additional candidate motion information by usinguni-directional motion information of one temporal prediction unitselected from the direction of the direction L0 and the direction of thedirection L1.

The generating of the additional candidate motion information mayinclude, when motion information of the available spatial predictionunits and motion information of the available temporal prediction unitsinclude uni-directional motion information of one temporal predictionunit selected from the direction of the direction L0 and the directionof the direction L1, generating the additional candidate motioninformation by using bi-directional motion information obtained bycombining the prediction of the direction L0 and the prediction of thedirection L1.

The generating of the additional candidate motion information mayinclude, when motion information of the available spatial predictionunits and motion information of the available temporal prediction unitsinclude uni-directional motion information of one selected from thedirection of the direction L0 and the direction of the direction L1,generating bi-directional motion information by combininguni-directional motion information including a motion vector having apredetermined component value, as the additional candidate motioninformation.

In addition, the generating of the additional candidate motioninformation may include generating a reference picture having areference picture index having a predetermined value as the additionalcandidate motion information.

In the generating of the additional candidate motion information,whether default candidate motion information and the generatedadditional candidate motion information are duplicated may not bechecked, and the generated additional candidate motion information maybe added to candidate motion information.

According to another aspect of one or more exemplary embodiments, thereis provided an apparatus for encoding motion information, including acandidate motion information generating unit for performing motionprediction on a current prediction unit to obtain motion informationabout the current prediction unit, for determining whether motioninformation of spatial prediction units that are spatially collocated toa current prediction unit and motion information of temporal predictionunits that are temporally collocated to the current prediction unit areavailable, and as a result of the determining, when the number of themotion information of the spatial prediction units and the motioninformation of the temporal prediction units is less than apredetermined number ‘n’ (where n is an integer), for generatingadditional candidate motion information by using the available motioninformation of the spatial prediction units and the motion informationof the temporal prediction units such that the total number of pieces ofcandidate motion information is ‘n’; and a motion information encoderfor encoding motion information of the current prediction unit by usingthe ‘n’ pieces of motion information.

According to another aspect of one or more exemplary embodiments, thereis provided a method of decoding motion information, includingdetermining whether motion information of spatial prediction units thatare spatially collocated to a current prediction unit and motioninformation of temporal prediction units that are temporally collocatedto the current prediction unit are available; as a result of thedetermining, when the number of the motion information of the spatialprediction units and the motion information of the temporal predictionunits is less than a predetermined number ‘n’ (where n is an integer),generating additional candidate motion information by using theavailable motion information of the spatial prediction units and themotion information of the temporal prediction units such that the totalnumber of pieces of candidate motion information is ‘n’; obtaining indexinformation indicating single motion information from among the ‘n’pieces of candidate motion information from a bitstream; and obtainingmotion information of the current prediction unit by using motioninformation indicated by the index.

According to another aspect one or more exemplary embodiments, there isprovided an apparatus for decoding motion information, including agenerating unit for determining whether motion information of spatialprediction units that are spatially collocated to a current predictionunit and motion information of temporal prediction units that aretemporally collocated to the current prediction unit are available, andas a result of the determining, when the number of the motioninformation of the spatial prediction units and the motion informationof the temporal prediction units is less than a predetermined number ‘n’(where n is an integer), for generating additional candidate motioninformation by using the available motion information of the spatialprediction units and the motion information of the temporal predictionunits such that the total number of pieces of candidate motioninformation is ‘n’; an entropy decoder for obtaining index informationindicating single motion information from among the ‘n’ pieces ofcandidate motion information from a bitstream; and a motion informationdecoder for obtaining motion information of the current prediction unitby using motion information indicated by the index.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus for encoding a video,according to an exemplary embodiment;

FIG. 2 is a block diagram of an apparatus for decoding a video,according to an exemplary embodiment;

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 4 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment;

FIG. 5 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment;

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment;

FIG. 7 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1;

FIG. 14 is a block diagram of a motion information encoding apparatusaccording to an exemplary embodiment;

FIG. 15 is a block diagram of a candidate motion information generatingunit of FIG. 14, according to an exemplary embodiment;

FIG. 16 illustrates adjacent prediction units that are spatiallycollocated to a current prediction unit, according to an exemplaryembodiment;

FIG. 17A is a reference diagram for explaining a process for determininga scaled spatial prediction motion vector candidate, according to anexemplary embodiment;

FIG. 17B is a reference diagram for explaining a process for generatingadditional candidate motion information by using a prediction unit thatis spatially collocated to a current prediction unit, according to anexemplary embodiment;

FIG. 18 is a reference diagram for explaining a method of generating aprediction motion vector candidate of a current prediction unit byscaling a motion vector of an adjacent prediction unit, according to anexemplary embodiment;

FIG. 19 is a reference diagram for explaining a process of generatingtemporal candidate motion information, according to an exemplaryembodiment;

FIGS. 20A and 20B are diagrams for explaining a process of generatingadditional candidate motion information by using motion information ofavailable prediction units, according to another exemplary embodiment;

FIGS. 21A and 21B are diagrams for describing a positional relationshipbetween a current picture and a reference picture when additionalcandidate motion information of FIGS. 20A and 20B is generated,according to an exemplary embodiment;

FIG. 22 is a flowchart of a method of encoding a motion vector,according to an exemplary embodiment;

FIG. 23 is a block diagram of a motion vector decoding apparatusaccording to an exemplary embodiment; and

FIG. 24 is a flowchart of a method of decoding motion information,according to an exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, one or more exemplary embodiments will be described morefully with reference to the accompanying drawings.

FIG. 1 is a block diagram of a video encoding apparatus 100, accordingto an exemplary embodiment.

The video encoding apparatus 100 includes a maximum coding unit splitter110, a coding unit determiner 120, and an output unit 130.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit for the current picture of an image. If thecurrent picture is larger than the maximum coding unit, image data ofthe current picture may be split into the at least one maximum codingunit. The maximum coding unit according to an exemplary embodiment maybe a data unit having a size of 32×32, 64×64, 128×128, 256×256, etc.,wherein a shape of the data unit is a square having a width and lengthin squares of 2. The image data may be output to the coding unitdeterminer 120 according to the at least one maximum coding unit.

A coding unit according to one or more exemplary embodiments may becharacterized by a maximum size and a depth. The depth denotes a numberof times the coding unit is spatially split from the maximum codingunit, and as the depth deepens, deeper encoding units according todepths may be split from the maximum coding unit to a minimum codingunit. A depth of the maximum coding unit is an uppermost depth and adepth of the minimum coding unit is a lowermost depth. Since a size of acoding unit corresponding to each depth decreases as the depth of themaximum coding unit deepens, a coding unit corresponding to an upperdepth may include a plurality of coding units corresponding to lowerdepths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to one or more exemplary embodiments is split according todepths, the image data of a spatial domain included in the maximumcoding unit may be hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. Thus, the encoded image data of the coding unitcorresponding to the determined coded depth is finally output. Also, thecoding units corresponding to the coded depth may be regarded as encodedcoding units. The determined coded depth and the encoded image dataaccording to the determined coded depth are output to the output unit130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or smallerthan the maximum depth, and results of encoding the image data arecompared based on each of the deeper coding units. A depth having theleast encoding error may be selected after comparing encoding errors ofthe deeper coding units. At least one coded depth may be selected foreach maximum coding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to a same depthin one maximum coding unit, it is determined whether to split each ofthe coding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the image data is split into regions according to thedepths and the encoding errors may differ according to regions in theone maximum coding unit, and thus the coded depths may differ accordingto regions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be divided according to coding units of at least onecoded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an exemplary embodimentinclude coding units corresponding to a depth determined to be the codeddepth, from among all deeper coding units included in the maximum codingunit. A coding unit of a coded depth may be hierarchically determinedaccording to depths in the same region of the maximum coding unit, andmay be independently determined in different regions. Similarly, a codeddepth in a current region may be independently determined from a codeddepth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of times splitting is performed from a maximum coding unitto a minimum coding unit. A first maximum depth according to anexemplary embodiment may denote the total number of times splitting isperformed from the maximum coding unit to the minimum coding unit. Asecond maximum depth according to an exemplary embodiment may denote thetotal number of depth levels from the maximum coding unit to the minimumcoding unit. For example, when a depth of the maximum coding unit is 0,a depth of a coding unit, in which the maximum coding unit is splitonce, may be set to 1, and a depth of a coding unit, in which themaximum coding unit is split twice, may be set to 2. Here, if theminimum coding unit is a coding unit in which the maximum coding unit issplit four times, 5 depth levels of depths 0, 1, 2, 3 and 4 exist, andthus the first maximum depth may be set to 4, and the second maximumdepth may be set to 5.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit. Transformation may be performed according to a method oforthogonal transformation or integer transformation.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split into coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partitiontype include symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit.

In order to perform the transformation in the coding unit, thetransformation may be performed based on a data unit having a sizesmaller than or equal to the coding unit. For example, the data unit forthe transformation may include a data unit for an intra mode and a dataunit for an inter mode.

A data unit used as a base of the transformation will now be referred toas a ‘transformation unit’. Similarly to the coding unit, thetransformation unit in the coding unit may be recursively split intosmaller sized regions, so that the transformation unit may be determinedindependently in units of regions. Thus, residual data in the codingunit may be divided according to the transformation unit having the treestructure according to transformation depths.

A transformation depth indicating the number of times splitting isperformed to reach the transformation unit by splitting the height andwidth of the coding unit may also be set in the transformation unit. Forexample, in a current coding unit of 2N×2N, a transformation depth maybe 0 when the size of a transformation unit is 2N×2N, may be 1 when thesize of a transformation unit is N×N, and may be 2 when the size of atransformation unit is N/2×N/2. That is, the transformation unit havingthe tree structure may also be set according to transformation depths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to a predictionunit, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit anda method of determining a partition, according to one or more exemplaryembodiments, will be described in detail later with reference to FIGS. 3through 12.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using rate-distortion optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit may be a maximumrectangular data unit that may be included in all of the coding units,prediction units, partition units, and transformation units included inthe maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode. Also, information about a maximum size of the codingunit defined according to pictures, slices, or GOPs, and informationabout a maximum depth may be inserted into a header of a bitstream.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit of thecurrent depth having the size of 2N×2N may include a maximum number of 4coding units of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having high resolution or a large data amount isencoded using conventional macroblocks, the number of macroblocks perpicture excessively increases. Accordingly, a number of pieces ofcompressed information generated for each macroblock increases, and thusit is difficult to transmit the compressed information and datacompression efficiency decreases. However, by using the video encodingapparatus 100, image compression efficiency may be increased since acoding unit is adjusted based on characteristics of an image, forexample, increasing a maximum size of a coding unit based on a size ofthe image.

FIG. 2 is a block diagram of a video decoding apparatus 200, accordingto an exemplary embodiment.

The video decoding apparatus 200 includes a receiver 210, an image dataand encoding information extractor 220, and an image data decoder 230.Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for various operations of the video decoding apparatus200 are identical to those described with reference to FIG. 1 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractinformation about a maximum size of a coding unit of a current picture,from a header about the current picture.

Also, the image data and encoding information extractor 220 extractsinformation about a coded depth and an encoding mode for the codingunits having a tree structure according to each maximum coding unit,from the parsed bitstream. The extracted information about the codeddepth and the encoding mode is output to the image data decoder 230. Inother words, the image data in a bit stream is split into the maximumcoding unit so that the image data decoder 230 decodes the image datafor each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include prediction includingintra prediction and motion compensation, and inverse transformation.Inverse transformation may be performed according to a method of inverseorthogonal transformation or inverse integer transformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

Also, the image data decoder 230 may perform inverse transformationaccording to each transformation unit in the coding unit, based on theinformation about the size of the transformation unit of the coding unitaccording to coded depths, so as to perform the inverse transformationaccording to maximum coding units.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to the each coded depth in thecurrent maximum coding unit by using the information about the partitiontype of the prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth, and output the image data of the current maximum coding unit.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode.

The video decoding apparatus 200 may obtain information about at leastone coding unit that generates the minimum encoding error when encodingis recursively performed for each maximum coding unit, and may use theinformation to decode the current picture. In other words, the codingunits having the tree structure determined to be the optimum codingunits in each maximum coding unit may be decoded. Also, the maximum sizeof coding unit is determined considering resolution and an amount ofimage data.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit, according to an exemplaryembodiment, will now be described with reference to FIGS. 3 through 13.

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 3 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe video data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened up to two layers by splitting the maximum codingunit up to two times. Meanwhile, since the maximum depth of the videodata 330 is 1, coding units 335 of the video data 330 may include amaximum coding unit having a long axis size of 16, and coding unitshaving a long axis size of 8 since depths are deepened up to one layerby splitting the maximum coding unit up to one time.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened up to 3 layers by splitting the maximumcoding unit up to three times. As a depth deepens, detailed informationmay be precisely expressed.

FIG. 4 is a block diagram of an image encoder 400 based on coding units,according to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 performs inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 perform operations based on each coding unitfrom among coding units having a tree structure while considering themaximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

FIG. 5 is a block diagram of an image decoder 500 based on coding units,according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data, which ispost-processed through the deblocking unit 570 and the loop filteringunit 580, may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after operations of the parser 510 areperformed.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra prediction 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200may use hierarchical coding units so as to consider characteristics ofan image. A maximum height, a maximum width, and a maximum depth ofcoding units may be adaptively determined according to thecharacteristics of the image, or may be differently set by a user. Sizesof deeper coding units according to depths may be determined accordingto the predetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. Since a depthdeepens along a vertical axis of the hierarchical structure 600, aheight and a width of the deeper coding unit are each split. Also, aprediction unit and partitions, which are bases for prediction encodingof each deeper coding unit, are shown along a horizontal axis of thehierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, a coding unit 640having a size of 8×8 and a depth of 3, and a coding unit 650 having asize of 4×4 and a depth of 4 exist. The coding unit 650 having the sizeof 4×4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e. a partition in the coding unit610 having a size of 64×64, partitions 612 having the size of 64×32,partitions 614 having the size of 32×64, or partitions 616 having thesize of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition in the coding unit 620 having a sizeof 32×32, partitions 622 having a size of 32×16, partitions 624 having asize of 16×32, and partitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

The coding unit 650 having the size of 4×4 and the depth of 4 is theminimum coding unit and a coding unit of the lowermost depth. Aprediction unit of the coding unit 650 may be split into partitionsincluded in the coding unit 650, i.e. a partition having a size of 4×4included in the coding unit 650, partitions 652 having a size of 4×2,partitions 654 having a size of 2×4, and partitions 656 having a size of2×2.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths and performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 7 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The video encoding apparatus 100 encodes or the video decoding apparatusdecodes an image according to coding units having sizes smaller than orequal to a maximum coding unit for each maximum coding unit. Sizes oftransformation units for transformation during encoding may be selectedbased on data units that are not larger than a corresponding codingunit.

For example, in the video encoding apparatus 100 or the video decodingapparatus 200, if a size of the coding unit 710 is 64×64, transformationmay be performed by using the transformation units 720 having a size of32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_(—)0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second intra transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_(—)0×2N_(—)0 may include partitions of apartition type 912 having a size of 2N_(—)0×2N_(—)0, a partition type914 having a size of 2N_(—)0×N_(—)0, a partition type 916 having a sizeof N_(—)0×2N_(—)0, and a partition type 918 having a size ofN_(—)0×N_(—)0. FIG. 9 only illustrates the partition types 912 through918 which are obtained by symmetrically splitting the prediction unit910, but a partition type is not limited thereto, and the partitions ofthe prediction unit 910 may include asymmetrical partitions, partitionshaving a predetermined shape, and partitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_(—)0×2N_(—)0, two partitions having a size of 2N_(—)0×N_(—)0,two partitions having a size of N_(—)0×2N_(—)0, and four partitionshaving a size of N_(—)0×N_(—)0, according to each partition type. Theprediction encoding in an intra mode and an inter mode may be performedon the partitions having the sizes of 2N_(—)0×2N_(—)0, N_(—)0×2N_(—)0,2N_(—)0×N_(—)0, and N_(—)0×N_(—)0. The prediction encoding in a skipmode is performed only on the partition having the size of2N_(—)0×2N_(—)0.

If an encoding error is smallest in one of the partition types 912through 916 having the sizes of 2N_(—)0×2N_(—)0, 2N_(—)0×N_(—)0, andN_(—)0×2N_(—)0, the prediction unit 910 may not be split into a lowerdepth.

If the encoding error is the smallest in the partition type 918 havingthe size of N_(—)0×N_(—)0, a depth is changed from 0 to 1 to split thepartition type 918 in operation 920, and encoding is repeatedlyperformed on coding units 930 having a depth of 2 and a size ofN_(—)0×N_(—)0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_(—)1×2N_(—)1 (=N_(—)0×N_(—)0) may includepartitions of a partition type 942 having a size of 2N_(—)1×2N_(—)1, apartition type 944 having a size of 2N_(—)1×N_(—)1, a partition type 946having a size of N_(—)1×2N_(—)1, and a partition type 948 having a sizeof N_(—)1×N_(—)1.

If an encoding error is the smallest in the partition type 948 havingthe size of N_(—)1×N_(—)1, a depth is changed from 1 to 2 to split thepartition type 948 in operation 950, and encoding is repeatedlyperformed on coding units 960, which have a depth of 2 and a size ofN_(—)2×N_(—)2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 having the size of N_(d−1)×N_(d−1) hasthe minimum encoding error, since a maximum depth is d, a coding unitCU_(d−1) having a depth of d−1 is no longer split to a lower depth, anda coded depth for the coding units constituting a current maximum codingunit 900 is determined to be d−1 and a partition type of the currentmaximum coding unit 900 may be determined to be N_(d−1)×N_(d−1). Also,since the maximum depth is d and a minimum coding unit 980 having alowermost depth of d−1 is no longer split to a lower depth, splitinformation for the minimum coding unit 980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be arectangular data unit obtained by splitting a minimum coding unit 980 by4. By performing the encoding repeatedly, the video encoding apparatus100 may select a depth having the least encoding error by comparingencoding errors according to depths of the coding unit 900 to determinea coded depth, and set a corresponding partition type and a predictionmode as an encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits. In other words, partition types in the coding units 1014, 1022,1050, and 1054 have a size of 2N×N, partition types in the coding units1016, 1048, and 1052 have a size of N×2N, and a partition type of thecoding unit 1032 has a size of N×N. Prediction units and partitions ofthe coding units 1010 are smaller than or equal to each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Information 0 Split (Encoding on Coding Unit having Sizeof 2N × 2N and Current Depth of d) Information 1 Prediction PartitionType Size of Transformation Unit Repeatedly Mode Encode IntraSymmetrical Asymmetrical Split Split Coding Units Inter PartitionPartition Information 0 of Information 1 of having Skip Type TypeTransformation Transformation Lower Depth (Only Unit Unit of d + 1 2N ×2N) 2N × 2N 2N × nU 2N × 2N N × N 2N × N 2N × nD (Symmetrical N × 2N nL× 2N Type) N × N nR × 2N N/2 × N/2 (Asymmetrical Type)

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred to for predictingthe current coding unit.

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to the encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1328 having a size of N×N,a partition type 1332 having a size of 2N×nU, a partition type 1334having a size of 2N×nD, a partition type 1336 having a size of nL×2N,and a partition type 1338 having a size of nR×2N.

When the partition type is set to be symmetrical, i.e. the partitiontype 1322, 1324, 1326, or 1328, a transformation unit 1342 having a sizeof 2N×2N is set if split information (TU size flag) of a transformationunit is 0, and a transformation unit 1344 having a size of N×N is set ifa TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Hereinafter, motion prediction and motion compensation, which areperformed by the motion estimator 420 and the motion compensator 425 ofthe video encoding apparatus 100 of FIG. 4 and the motion compensator550 of the video decoding apparatus 200 of FIG. 5, and processes ofencoding and decoding motion information, which are performed by theentropy encoder 450 of FIG. 4 and the entropy decoder 520 of FIG. 5,will be described. As described with reference to FIGS. 1 through 13, aprediction unit is a data unit for prediction encoding of a coding unit.Hereinafter, the prediction unit refers to the prediction unit itself ora partition obtained by splitting the prediction unit.

As described above, prediction units are encoded by using variousprediction modes such as an intra prediction mode, an inter mode, and askip mode.

In the inter prediction mode, a current prediction unit is predicted viauni-direction prediction or bi-directional prediction. In detail, aprediction unit included in a P slice is predicted via uni-directionprediction using only one of a reference picture ‘L0 picture’ includedin a reference picture list ‘List 0’ and a reference picture ‘L1picture’ included in a reference picture list ‘List 1’. A predictionmethod using the reference picture ‘L0 picture’ included in thereference picture list ‘List 0’ is referred to as “L0 prediction”. Aprediction method using the reference picture ‘L1 picture’ included inthe reference picture list ‘List 1’ is referred to as “L1 prediction”.In the reference picture list ‘List 0’, a reference picture index isassigned in order from a latest past picture to a previous picturethereto and then is assigned in order from a closest future picture to anext picture thereafter. On the other hand, in the reference picturelist ‘list 1’, a reference picture index is assigned in order from aclosest future picture to a next picture thereafter and then is assignedin order from a latest past picture to a previous picture thereto.

A prediction unit included in a B slice is predicted via uni-directionprediction or bi-directional prediction using an average of thereference picture ‘L0 picture’ included in the reference picture list‘List 0’ and the reference picture ‘L1 picture’ included in thereference picture list ‘list 1’. A bi-direction predictive modeperformed by the motion estimator 420 may use two reference picturesrather than being limited to a previous or next reference picture of acurrent picture and may be referred to as a bi-predictive mode.

Costs obtained by encoding prediction values obtained according to theprediction modes are compared with each other and a prediction modehaving a smallest cost is determined as a final prediction mode of acurrent prediction unit. When the costs are compared with each other,the final prediction mode to be applied to the current prediction unitmay be determined based on rate-distortion.

In order for a decoding side to generate a prediction value of aprediction unit on which inter prediction is performed, referencepicture information about a picture referred to for every predictionunit on which inter prediction is performed, motion vector information,and motion information such as a prediction direction may be transmittedto the decoding side. According to one or more exemplary embodiments, inorder to reduce transmission overhead, the motion information is encodedbased on motion information that is predicted by using motioninformation of an adjacent prediction unit that is previously encoded orby using a prediction unit collocated to a current prediction unit inthe previous picture, rather than being encoded without changes.

According to one or more exemplary embodiments, there are providedvarious methods of additionally generating candidate motion informationsuch that the total number of pieces of motion information is equal to apredetermined number when the number of pieces of default motioninformation obtained from a prediction unit that is spatially andtemporally collocated to a current prediction unit that is previouslydetermined by an encoding side and a decoding side is smaller than thepredetermined number. According to one or more exemplary embodiments,the same method may be previously determined from among the variousmethods of additionally generating candidate motion information by theencoding side and the decoding side. In this case, respectivepredetermined indexes indicating the various methods of additionallygenerating candidate motion information may be set. In addition, anindex indicating a method of additionally generating candidate motioninformation, which is used for encoding, may be added to a sequenceparameter set (SPS), a picture parameter set (PPS), or a slice headerand may be transmitted.

Throughout this specification, one or more exemplary embodiments will bedescribed in terms of a case where motion vector information as motioninformation is encoded. However, exemplary embodiments are not limitedthereto. Alternatively, one or more exemplary embodiments may be appliedto a case where motion information other than motion vector information,such as reference picture information and prediction directioninformation is encoded.

Hereinafter, a method and apparatus for encoding motion information of aprediction unit, and a method and apparatus for decoding motioninformation of a prediction unit will be described in detail with regardto one or more exemplary embodiments.

FIG. 14 is a block diagram of a motion information encoding apparatus1400 according to an exemplary embodiment. Referring to FIG. 14, themotion information encoding apparatus 1400 includes a candidate motioninformation generating unit 1410, i.e. a candidate motion informationgenerator, and a motion information encoder 1420. The motion informationencoding apparatus 1400 of FIG. 14 may be included in the image encoder400 of FIG. 4. For example, the motion estimator 420 of FIG. 4 mayperform a function of the candidate motion information generating unit1410 of FIG. 14 and the entropy encoder 450 of FIG. 4 may perform afunction of the motion information encoder 1420 of FIG. 14. Exemplaryembodiments are not limited thereto. Other components or a controller(not shown) of the image encoder 400 of FIG. 4 may perform a function ofthe motion information encoding apparatus 1400 of FIG. 14. The candidatemotion information generating unit 1410 obtains candidate motioninformation by using motion information of adjacent prediction unitsthat are temporally and spatially collocated to a current predictionunit. In particular, the candidate motion information generating unit1410 obtains default candidate motion information from adjacentprediction units that are spatially collocated to the current predictionunit that is previously set and prediction units that are temporallycollocated to the current prediction unit that is previously set. If thenumber of pieces of default candidate motion information is smaller thana predetermined number n (where n is an integer), i.e. a threshold, thecandidate motion information generating unit 1410 generates ‘n’ piecesof candidate motion information by modifying or combining motioninformation of prediction units that are spatially collocated to thecurrent prediction and motion information of prediction units that aretemporally collocated to the current prediction or adding motioninformation having a predetermined value such that the total number ofpieces of candidate motion information may be ‘n’. A process ofgenerating candidate motion information will be described later.

The motion information encoder 1420 determines motion information aboutthe current prediction unit from among the ‘n’ pieces of candidatemotion information and encodes index information indicating thedetermined motion information as motion information of the currentprediction unit. In detail, the motion information encoder 1420 assigns0 to (n−1) motion information indexes to the ‘n’ pieces of candidatemotion information, respectively, and encodes an index corresponding tomotion information of the current prediction unit as motion informationof the current prediction unit. For example, when motion informationcorresponds to a prediction motion vector and n=2, that is, when thenumber of prediction motion vector candidates of the current predictionunit is fixed to 2, if two prediction motion vector candidates that arerespectively generated with respect to a direction L0 and a direction L1by the candidate motion information generating unit 1410 are MVLX_Cand0and MVLX_Cand1 (X is 0 or 1), respectively, the motion informationencoder 1420 sets a prediction motion vector index indicating MVLX_Cand0to 0 and sets a prediction motion vector index indicating MVLX_Cand1 to1 and encodes an index corresponding to a prediction motion vectorhaving a minimum cost as motion vector information of the currentprediction unit according to the encoding result of the currentprediction unit.

The motion information encoder 1420 may encode reference pictureinformation, prediction direction information, and a difference valuebetween the prediction motion vector and an original motion vector ofthe current prediction unit, in addition to the prediction motion vectorindex, and may add the encoded information to a bitstream.

When the encoding side obtains a fixed number of pieces of candidatemotion information under a predetermined rule and transmits indexinformation indicating a single piece of motion information from amongthe pieces of candidate motion information, the decoding side maygenerate a fixed number of pieces of candidate motion information underthe same rule as that of the encoding side and may determine motioninformation of the current prediction unit by using the transmittedindex information. Like in the above-described example, when the motioninformation corresponds to a prediction motion vector, the decoding sidemay obtain an index indicating the prediction motion vector and adifference value between a motion vector and the prediction motionvector from a bitstream and may restore the motion vector of the currentprediction unit by adding the difference value with the predictionmotion vector indicated by the prediction motion vector index. Inaddition, the decoding side may generate a prediction value of thecurrent prediction unit by using the restored motion vector, and thereference picture information and the prediction direction information(directions L0 and L1) which are obtained from a bitstream.

FIG. 15 is a block diagram of the candidate motion informationgenerating unit 1410 of FIG. 14, according to an exemplary embodiment.

Referring to FIG. 15, the candidate motion information generating unit1410 includes a spatial candidate motion information generating unit1510, a temporal candidate motion information generating unit 1520, aredundancy removing unit 1530, and an additional candidate motioninformation generating unit 1540.

The spatial candidate motion information generating unit 1510 generatescandidate motion information by using motion information of predictionunits that are spatially collocated to the current prediction unit. Indetail, the spatial candidate motion information generating unit 1510includes an upper candidate motion information generating unit 1511 thatsequentially searches adjacent prediction units positioned above thecurrent prediction unit in a predetermined order to obtain motioninformation, and a left candidate motion information generating unit1512 that sequentially searches adjacent prediction units positioned onthe left of the current prediction unit in a predetermined order toobtain motion information.

FIG. 16 illustrates adjacent prediction units that are spatiallycollocated to a current prediction unit, according to an exemplaryembodiment. Exemplary embodiments are not limited to the case shown inFIG. 16. For example, adjacent prediction units of different spatiallocations may be used as adjacent prediction units that are spatiallycollocated to a current prediction unit used to predict motioninformation of a current prediction unit.

Referring to FIG. 16, the spatial candidate motion informationgenerating unit 1510 searches a left-bottom adjacent prediction unit A01621 positioned on the left-bottom of the current prediction unit 1610and a left-down adjacent prediction unit A1 1622 positioned above theleft-bottom adjacent prediction unit A0 1621 from among adjacentprediction units positioned on the left of a current prediction unit1610 in a predetermined scanning order, and determines motioninformation of a first prediction unit having available motioninformation, which is first searched, as left candidate motioninformation, from among the left-bottom adjacent prediction unit A0 1621and the left-down adjacent prediction unit A1 1622. In addition, thespatial candidate motion information generating unit 1510 searches anadjacent prediction unit B0 1631 positioned on the above-right of thecurrent prediction unit 1610, an adjacent prediction unit B1 1632positioned on the left of the adjacent prediction unit B0 1631, and anadjacent prediction unit B2 1633 positioned on the above-left of thecurrent prediction unit 1610 from among adjacent prediction unitspositioned above the current prediction unit 1610, and determines motioninformation of a prediction unit having available motion information,which is first searched, as upper candidate motion information.Likewise, the spatial candidate motion information generating unit 1510does not search all prediction units positioned around the currentprediction unit 1610 and searches default adjacent prediction units,that is, the adjacent predictions units A0, A1, B0, B1, and B2 to obtainmotion information, thereby reducing calculation complexity. Asdescribed above, the number and locations of adjacent prediction unitsthat are searched to obtain spatial candidate motion information may bechanged. However, in order for a decoding side to restore motioninformation of the current prediction unit, the number and locations ofadjacent prediction units that are searched to obtain spatial candidatemotion information in an encoding side and the decoding side may bepreviously set.

As an example of a process for determining motion information, a processfor determining a prediction motion vector of a motion vector of acurrent prediction unit from adjacent prediction units that arespatially collocated to the current prediction unit will be described.

Referring to FIGS. 15 and 16, the left candidate motion informationgenerating unit 1512 sequentially checks whether motion vectors of theleft-bottom adjacent prediction unit A0 1621 and the left-down adjacentprediction unit A1 1622 are available and determines a motion vector ofan adjacent prediction unit having an available motion vector as a leftcandidate motion vector. Here, the availability of a motion vectorrefers to whether an adjacent prediction unit has a motion vectorindicating the same reference picture in the same reference picture listas a current prediction unit. For example, when a motion vector of thecurrent prediction unit 1610 is a motion vector indicating a referencepicture (L0R0 picture) having a reference index R0 in a list L0, if theleft-bottom adjacent prediction unit A0 1621 is a prediction unit onwhich intra prediction is performed, or has a motion vector indicating areference picture included in a different reference picture list fromthe current prediction unit 1610, or has a motion vector indicating adifferent reference picture included in the same reference picture asthe current prediction unit 1610, it is determined that the left-bottomadjacent prediction unit A0 1621 does not have an available motionvector. If the left-down adjacent prediction unit A1 1622 has a motionvector indicating the same picture in the same reference picture list asthe current prediction unit 1610, the motion vector of the left-downadjacent prediction unit A1 1622 is determined as a left candidatemotion vector.

Similarly, the upper candidate motion information generating unit 1511sequentially checks whether motion vectors of the adjacent predictionunit B0 1631, the adjacent prediction unit B1 1632, and the adjacentprediction unit B2 1633 are available and determines a motion vector ofan adjacent prediction unit indicating the same reference picture in thesame reference picture list as the current prediction unit 1610 as anupper candidate motion vector.

When adjacent prediction units having an available motion vector do notexist from among adjacent prediction units, the spatial candidate motioninformation generating unit 1510 may scale a motion vector of anadjacent prediction unit indicating a different reference picture of thesame reference picture list as the current prediction unit 1610 or amotion vector of an adjacent prediction unit indicating a referencepicture included in a different reference picture list from the currentprediction unit 1610 and may use the scaled motion vector as aprediction motion vector candidate of the current prediction unit 1610.

FIG. 17A is a reference diagram for explaining a process for determininga scaled spatial prediction motion vector candidate, according to anexemplary embodiment.

Referring to FIG. 17A, a motion vector MVL0_Cur of a current predictionunit 1731 indicates an L0R0 picture 1720 that is a reference picturehaving a reference index R0 in a list L0, the left-bottom adjacentprediction unit A0 1621 has a prediction motion on which intraprediction is performed, the left-down adjacent prediction unit A1 1622has a motion vector mvL1_A1 indicating an L1R0 picture 1740 that is areference picture having a reference index R0 in a list L1, the adjacentprediction unit B0 1631 has a prediction unit on which intra predictionis performed, the adjacent prediction unit B1 1632 has a motion vectormvL1_B1 indicating an L1R1 picture 1750 that is a reference picturehaving a reference index R1 in a list L1, and adjacent prediction unitB2 1633 has a motion vector mvL0_B2 indicating an L0R1 picture 1710 thatis a reference picture having a reference index R1 in a list L0. In FIG.17A, any prediction unit from among adjacent prediction units of thecurrent prediction unit 1731 does not have the same motion vectorindicating the L0R0 picture 1720 as the motion vector MVL0_Cur of thecurrent prediction unit 1731. When an adjacent prediction unit having amotion vector indicating the same reference picture as a referencepicture indicated by a motion vector of the current prediction unit 1731does not exist from among adjacent prediction units, the spatialcandidate motion information generating unit 1510 may scale a motionvector of a prediction unit on which inter prediction is performed, fromamong adjacent prediction units, based on a temporal distance between areference picture indicated by a motion vector of a prediction unit onwhich inter prediction is performed and a reference picture indicated bya motion vector of a current prediction unit and may add the scaledmotion vector to a candidate motion vector. That is, the spatialcandidate motion information generating unit 1510 may add a motionvector of an adjacent prediction unit indicating a reference picturehaving a different reference index in the same reference picture list asthe current prediction unit 1731 from among motion vectors of anadjacent prediction unit to a candidate motion vector. In addition, whena motion vector of an adjacent prediction unit indicating a referencepicture having a different reference index in the same reference picturelist as the current prediction unit 1731 does not exist from amongmotion vectors of an adjacent prediction unit, the spatial candidatemotion information generating unit 1510 may add a motion vector of anadjacent prediction unit indicating a reference picture in a differentreference picture list from the current prediction unit 1731 to thecandidate motion vector.

For example, the spatial candidate motion information generating unit1510 may scale the motion vector mvL1_A1 of the left-down adjacentprediction unit A1 1622, except for the left-bottom adjacent predictionunit A0 1621 on which intra prediction is performed, in consideration ofa temporal distance between a current picture 1730 and the L0R0 picture1720 indicated by the motion vector MVL0_Cur of the current predictionunit 1731 and a temporal distance between the current picture 1730 andthe L1R0 picture 1740 indicated by the motion vector mvL1_A1 of theleft-down adjacent prediction unit A1 1622 and may determine the scaledmotion vector mvL1_A1′ (not shown) as a left motion vector candidate.

In addition, the spatial candidate motion information generating unit1510 may scale the motion vector mvL0_B2 of the adjacent prediction unitB2 1633 indicating the L0R1 picture 1710 that is a reference picturehaving a different reference index in the same reference picture as themotion vector MVL0_Cur of the current prediction unit 1731, instead ofthe motion vector mvL1_B1 of the adjacent prediction unit B1 1632indicating the L1R1 picture 1750 that is a reference picture in adifferent reference picture list from the current prediction unit 1731and determines the scaled motion vector mvL0_B2′ (not shown) as an uppermotion vector candidate. That is, when the spatial candidate motioninformation generating unit 1510 determines a motion vector of anadjacent prediction unit, which is subject to scaling, the spatialcandidate motion information generating unit 1510 may determine a motionvector of an adjacent prediction unit indicating a reference pictureincluded in the same reference picture list as a motion vector of acurrent prediction unit. Then, when a motion vector of an adjacentprediction unit indicating a reference picture included in the samereference picture list as the current prediction unit does not exist,the spatial candidate motion information generating unit 1510 maydetermine a motion vector of an adjacent prediction unit indicating areference picture included in a different reference picture list fromthe current prediction unit as a motion vector that is subject toscaling. The spatial candidate motion information generating unit 1510may scale the motion vector mvL0_B2 of the adjacent prediction unit B2in consideration of a temporal distance between the current picture 1730and the L0R0 picture 1720 indicated by the motion vector MVL0_Cur of thecurrent prediction unit 1731 and a temporal distance between the currentpicture 1730 and the LORI picture 1710 indicated by the motion vectormvL0_B2 of the adjacent prediction unit B2 1633 and may determine thescaled motion vector mvL0_B2′ as an upper motion vector candidate.

FIG. 18 is a reference diagram for explaining a method of generating aprediction motion vector candidate of a current prediction unit byscaling a motion vector of an adjacent prediction unit, according to anexemplary embodiment.

As described above, when the same motion vector as a current predictionunit, that is, a motion vector indicating a reference picture having thesame reference index included in the same reference picture list as thecurrent prediction unit does not exist from among adjacent predictionunits of the current prediction unit, a motion vector MV(Bn) of anadjacent prediction unit (a prediction unit Bn of FIG. 18) referring toa different reference picture in the same reference picture list as thecurrent prediction unit or a motion vector MV(An) of an adjacentprediction unit (a prediction unit An of FIG. 18) referring to areference picture included in a different reference picture list fromthe current prediction unit may be scaled, and the scaled motion vectormay be added to a prediction motion vector candidate of the currentprediction unit. In detail, when a temporal distance d(cur) between acurrent picture and a reference picture (an L0R0 picture) indicated bythe motion vector MVL0_Cur of a current prediction unit is d(cur) and atemporal distance between the current picture and a reference picture(an L0R1 picture) indicated by the motion vector MV(Bn) of a predictionunit Bn is d(Bn), the motion vector MV(Bn) of the prediction unit Bn maybe scaled according to Equation, MV(Bn)′=MV(Bn)*{d(cur)/d(Bn)}, and thescaled motion vector MV(Bn)′ may be added to a prediction motion vectorcandidate of the current prediction unit. Similarly, when a temporaldistance between a current picture and a reference picture (a L1R1picture) indicated by a motion vector MV(An) of a prediction unit An isd(An), the motion vector MV(An) of the prediction unit An may be scaledaccording to Equation, MV(An)′=MV(An)*{d(cur)/d(An)}, and the scaledmotion vector MV(An)′ may be added to a prediction motion vectorcandidate of the current prediction unit.

Whether the scaled motion vector is included in a spatial motion vectorcandidate may be determined in consideration of a predeterminedcondition. For example, the spatial candidate motion informationgenerating unit 1510 may scale a motion vector of a prediction unit onwhich inter prediction is performed, from among the adjacent predictionunits B0, B1, and B2 and may add the scaled motion vector to an uppermotion vector candidate only when intra prediction is performed on oneof the adjacent prediction units A0 and A1 adjacent to the left of thecurrent prediction unit. In other words, whether the scaled motionvector is added to a spatial prediction motion vector candidate may beselectively performed according to whether a predetermined condition issatisfied. The predetermined condition may be designed in various waysand is not limited to the above-described example.

In the above-described example, when the spatial candidate motioninformation generating unit 1510 searches upper prediction units andleft prediction units that are spatially collocated to a currentprediction unit, the spatial candidate motion information generatingunit 1510 searches left adjacent prediction units in order of A0→A1 orsearches upper adjacent prediction units in order of B0→B1→B2. However,exemplary embodiments are not limited to the scanning order.Alternatively, the spatial candidate motion information generating unit1510 may determine adjacent prediction units in order of, for example,A1→B1→B0→A0→B2 without a basis such as an upper or left side and maydetermine whether motion information of each adjacent prediction unit isused as motion information of the current prediction unit.

In addition, when the spatial candidate motion information generatingunit 1510 generates spatial candidate motion information, the spatialcandidate motion information generating unit 1510 may check whethermotion information of all prediction units positioned above the currentprediction unit and on the left of the current prediction unit, forexample, of all of the adjacent predictions units A0, A1, B0, B1, and B2is available without any scanning order instead of searching adjacentprediction units in a predetermined scanning order and then may add allpieces of available motion information from among the motion informationof the adjacent predictions units A0, A1, B0, B1, and B2 to the spatialmotion information candidate.

Referring back to FIG. 15, the temporal candidate motion informationgenerating unit 1520 generates temporal candidate motion information byusing motion information of a motion unit that is temporally collocatedto a current prediction unit, that is, motion information of a motionunit that is collocated based on a location of the current predictionunit from among prediction units of a previous picture that ispreviously encoded.

FIG. 19 is a reference diagram for explaining a process of generatingtemporal candidate motion information, according to an exemplaryembodiment.

Referring to FIGS. 15 and 19, the temporal candidate motion informationgenerating unit 1520 may generate temporal candidate motion informationby using motion information of a prediction unit 1924 positioned on thebelow-right of a prediction unit 1921 of the reference picture 1920having the same location as a current prediction unit 1911 from amongprediction units of a reference picture 1920 that is previously encodedto a current picture 1910. For example, when motion information is aprediction motion vector, the temporal candidate motion informationgenerating unit 1520 may generate a temporal motion vector candidate byscaling a motion vector of the prediction unit 1924. The scaling of thetemporal prediction motion vector may be performed based on a temporaldistance between an L0R0 picture 1920 and a reference picture L1R0 1930and a temporal distance between the current picture 1910 and thereference picture L1R0 1930, as described with reference to FIG. 18.

If the prediction unit 1924 positioned on the below-right of theprediction unit 1921 is intra-predicted such that a motion vector of theprediction unit 1924 is not available, the temporal candidate motioninformation generating unit 1520 may scale a motion vector of theprediction unit 1921, which contains a point C′ 1922 of the referencepicture 1920 as the same location as a point C 1912 of a central pointof the current prediction unit 1911 and may generate the temporalprediction motion vector. That is, the temporal candidate motioninformation generating unit 1520 may first check whether motioninformation of a prediction unit positioned on the below-right of aprediction unit having the same location as a current prediction unitfrom among prediction units of a previous picture is available, maysequentially determine whether motion information of a prediction unitcontaining a point having the same location as a central point of thecurrent prediction unit is available, and then may add available motioninformation of a prediction unit to the temporal candidate motioninformation. The number and locations of prediction units of a previouspicture that is searched to generate the temporal candidate motioninformation may not be limited to the case shown in FIG. 19 and may bechanged in various ways. In addition, when the temporal candidate motioninformation generating unit 1520 generates temporal candidate motioninformation, the temporal candidate motion information generating unit1520 may not check whether motion information of prediction units of aprevious picture is available in a predetermined order, may check bothwhether motion information of a prediction unit positioned on thebelow-right of a prediction unit having the same location as a currentprediction unit is available and whether motion information of aprediction unit containing a point having the same location as a centralpoint of the current prediction unit is available, and then may add allof pieces of the available motion information of the prediction unit ofthe previous picture to the temporal candidate motion information.

Referring back to FIG. 15, the redundancy removing unit 1530 maydetermine whether the spatial candidate motion information and thetemporal candidate motion information are identical to each other andmay remove redundant motion information from the candidate motioninformation. The redundancy removing unit 1530 may be omitted in orderto reduce calculation complexity. That is, a process of checkingredundancy may be skipped.

The number of pieces of the candidate motion information generated bythe spatial candidate motion information generating unit 1510 and thetemporal candidate motion information generating unit 1520 may besmaller than a predetermined number ‘n’. In the above-described example,when intra prediction is performed on all adjacent prediction unitspositioned above the current prediction unit or on the left of thecurrent prediction unit or when intra prediction is performed onprediction units positioned in a predetermined location of previouspictures searched by the temporal candidate motion informationgenerating unit 1520, the number of pieces of the generated candidatemotion information may be less than ‘n’.

When the number of pieces of the generated candidate motion informationgenerated by the spatial candidate motion information generating unit1510 and the temporal candidate motion information generating unit 1520is less than a predetermined number ‘n’, the additional candidate motioninformation generating unit 1540 may generate additional candidatemotion information by using motion information of spatial predictionunits and available motion information of temporal prediction units suchthat the total number of pieces of candidate motion information may be‘n’.

Hereinafter various methods of generating additional candidate motioninformation via the additional candidate motion information generatingunit 1540 will be described.

When the spatial candidate motion information generating unit 1510sequentially checks whether adjacent prediction units of a currentprediction unit are available, the additional candidate motioninformation generating unit 1540 may generate additional candidatemotion information by using motion information of a prediction unit thatis checked after an available adjacent prediction unit that is firstchecked.

FIG. 17B is a reference diagram for explaining a process for generatingadditional candidate motion information by using a prediction unit thatis spatially collocated to a current prediction unit, according to anexemplary embodiment.

Referring to FIG. 17B, the additional candidate motion informationgenerating unit 1540 may generate motion information of a predictionunit from the adjacent prediction units A0, A1, B0, B1 and B2, whichhave available motion information but are not included in candidatemotion information because of being checked after another predictionunit that is previously scanned in a scanning order, as additionalcandidate motion information.

For example, it is assumed that left candidate motion informationgenerated by the spatial candidate motion information generating unit1510 is ‘Left’, upper candidate motion information generated by thespatial candidate motion information generating unit 1510 is ‘Above’,and temporal candidate motion information generated by the temporalcandidate motion information generating unit 1520 is ‘Temporal’. Theadditional candidate motion information generating unit 1540 determineswhether the candidate motion information (that is, Left, Above, andTemporal) is available, that is, whether the candidate motioninformation exists and determines that the number of pieces of thecandidate motion information is a predetermined number 3 (whichcorresponds to n=3). In addition, when the number of pieces of candidatemotion information is less than a predetermined number, the additionalcandidate motion information generating unit 1540 may generateadditional candidate motion information by using motion information of aprediction unit that is checked after an available adjacent predictionunit that is previously checked.

As described above, when the spatial candidate motion informationgenerating unit 1510 generates spatial candidate motion information, thespatial candidate motion information generating unit 1510 may checkwhether motion information of all prediction units positioned above thecurrent prediction unit and on the left of the current prediction unit,for example, of all of the adjacent predictions units A0, A1, B0, B1,and B2 is available without any scanning order and then may add allpieces of available motion information from among the motion informationof the adjacent predictions units A0, A1, B0, B1, and B2 to the spatialmotion information candidate. In this case, when the number of pieces ofcandidate motion information is less than a predetermined number, forexample, 5, the additional candidate motion information generating unit1540 may generate additional candidate motion information by usingmotion information of the available prediction unit.

It is assumed that left candidate motion information does not exist andmotion information of the adjacent prediction units B0, B1, and B2 isavailable. As shown in FIG. 17B, motion information of the adjacentprediction unit B0 that is previously checked in a scanning order isselected as upper candidate motion information and motion information ofthe adjacent prediction units B1 and B2 is not included in defaultmotion information. When the total number of pieces of candidate motioninformation is less than a predetermined number since the adjacentprediction units A0 and A1 do not have available motion information, theadditional candidate motion information generating unit 1540 may addmotion information of the adjacent prediction unit B1 or B2 toadditional candidate motion information.

Similarly, when upper candidate motion information does not exist andmotion information of the left adjacent prediction units A0 and A1 isavailable, motion information of the adjacent prediction unit A0 that ispreviously checked is selected as left motion information and motioninformation of the adjacent prediction unit A1 that is checked after theadjacent prediction unit A1 is not included in default motioninformation. However, when the number of pieces of candidate motioninformation is less than a predetermined number since the adjacentprediction units B0, B1, and B2 do not have available motioninformation, motion information of the adjacent prediction unit A1 maybe included in additional candidate motion information.

According to another exemplary embodiment, when the temporal candidatemotion information generating unit 1520 sequentially checks whetherprediction units of a previous picture that is temporally collocated toa current prediction unit are available, the additional candidate motioninformation generating unit 1540 may scale motion information of aprediction unit of a previous picture having motion information fromamong prediction units of the remaining previous picture except for afirst previous picture having available motion information and may addthe scaled motion information to additional candidate motioninformation.

Referring back to FIG. 19, the temporal candidate motion informationgenerating unit 1520 checks whether motion information of the predictionunit 1924 positioned on the right-bottom of the prediction unit 1921 ofthe reference picture 1920 having a corresponding location to thecurrent prediction unit 1911 is available from among prediction units ofthe reference picture 1920 that is previously encoded to the currentpicture 1910 and then determines whether motion information of theprediction unit 1921, which contains a point C′ 1922 of the referencepicture 1920 as the same location as a point C 1912 of a central pointof the current prediction unit 1911, is available. If the predictionunit 1924 positioned on the right-bottom of the prediction unit 1921 hasavailable motion information, motion information of the prediction unit1924 positioned on the right-bottom of the prediction unit 1921 isincluded in default candidate motion information and motion informationof the prediction unit 1921, which contains the point C′ 1922 of thereference picture 1920 as the same location as the point C 1912 is notincluded in default candidate motion information. When the total numberof pieces of candidate motion information is less than a predeterminednumber, the additional candidate motion information generating unit 1540may add motion information of the prediction unit 1921, which containsthe point C′ 1922 of the reference picture 1920 as the same location asthe point C 1912 to additional candidate motion information. That is,the additional candidate motion information generating unit 1540 may addmotion information of a prediction unit that is not included in defaultcandidate motion information from among prediction units of a previouspicture to additional candidate motion information.

According to another exemplary embodiment, the additional candidatemotion information generating unit 1540 may add motion informationhaving a predetermined value to additional candidate motion information.For example, when motion information is a prediction motion vector, ifthe number of pieces of candidate motion information is less than apredetermined number, the additional candidate motion informationgenerating unit 1540 may add a motion vector having a predeterminedcomponent value such as (0,0), (0,1), or (1,0) to a candidate motionvector.

According to another exemplary embodiment, when available motioninformation of spatial prediction units and temporal prediction unitscontains bi-directional motion vector information of prediction units ofthe directions L0 and L1, the additional candidate motion informationgenerating unit 1540 may add or subtract a predetermined offset to andfrom a motion vector of the prediction unit of the direction L0 and amotion vector of the prediction unit of the direction L1 to generateadditional candidate motion information.

FIGS. 20A and 20B are diagrams for explaining a process of generatingadditional candidate motion information by using motion information ofavailable prediction units, according to another exemplary embodiment.FIGS. 21A and 21B are diagrams for describing a positional relationshipbetween a current picture and a reference picture when additionalcandidate motion information of FIGS. 20A and 20B is generated,according to an exemplary embodiment.

Referring to FIGS. 20A and 21A, when the adjacent prediction unit B1from among prediction units positioned above a current prediction unithas a motion vector mvL0_B1 indicating an L0R0 picture 2110 that is areference picture of the prediction of the direction L0 and a motionvector mvL1_B1 indicating a L1R0 picture 2120 that is a referencepicture of the prediction of the direction L1, and a current picture2100 is positioned between the L0R0 picture 2110 and the L1R0 picture2120, the additional candidate motion information generating unit 1540may add predetermined offsets having the same absolute value anddifferent signs to the motion vector mvL0_B1 of the prediction of thedirection L0 and the motion vector mvL1_B1 of the prediction of thedirection L1 to generate a new motion vector and may add the new motionvector to additional candidate motion information. That is, as shown inFIG. 20A, the additional candidate motion information generating unit1540 may add a predetermined offset mv_offset to the motion vectormvL0_B1 of the prediction of the direction L0 such that a generatedmotion vector mvL0′ may be included in an additional candidate motionvector of the prediction of the direction L0 and may subtract the offsetmv_offset from the motion vector mvL1_B1 of the prediction of thedirection L1 such that generated motion vector mvL1′ may be included inadditional candidate motion vector of the prediction of the directionL1.

When a motion vector List0MV of the direction L0, which is included inbi-directional motion information obtained from an available adjacentprediction unit, has a value (mx0, my0) and a motion vector List1MV ofthe direction L1 has a value (mx1, my1), if a current picture ispositioned between a reference picture of the prediction of thedirection L1 and a reference picture of the prediction of the directionL0, the additional candidate motion information generating unit 1540 mayadd and subtract a predetermined offset to and from a motion vector ofthe prediction of the direction L0 and a motion vector of the predictionof the direction L1 to generate additional candidate motion informationas follows.

List0MV=(mx0+offset, my0), List1 MV=(mx0−offset, my0);

List0MV=(mx0−offset, my0), List1 MV=(mx0+offset, my0);

List0MV=(mx0, my0+offset), List1 MV=(mx0, my0−offset);

List0MV=(mx0, my0−offset), List1 MV=(mx0, my0+offset);

List0MV=(mx0+offset, my0+offset), List1 MV=(mx0−offset, my0−offset);

List0MV=(mx0+offset, my0−offset), List1 MV=(mx0−offset, my0+offset);

List0MV=(mx0−offset, my0+offset), List1 MV=(mx0+offset, my0−offset); and

List0MV=(mx0−offset, my0−offset), List1MV=(mx0+offset, my0+offset)

Referring to FIGS. 20B and 21B, when the adjacent prediction unit B1from among prediction units positioned above a current prediction unithas a motion vector mvL1R0_B1 indicating an L1R0 picture 2140 that is areference picture of the direction L0 and a motion vector mvL1R1_B1indicating an L1R1 picture 2150 that is a reference picture of thedirection L1, if the L1R0 picture 2140 and the L1R1 picture 2150 arepositioned on same locations with respect to a current picture 2130, theadditional candidate motion information generating unit 1540 may add orsubtract a predetermined offset to and from a motion vector mvL1R0_B1 ofthe prediction of the direction L0 and a motion vector mvL1R1_B1 of theprediction of the direction L1 to generate a new motion vector and mayadd the generated new motion vector to additional candidate motioninformation. That is, as shown in FIG. 20B, the additional candidatemotion information generating unit 1540 may add a motion vector mvL0′generated by adding an offset mv_offset to the motion vector mvL1R0_B1of the prediction of the direction L0 to an additional candidate motionvector of the prediction of the direction L0 and may add the motionvector mvL1′ generated by adding the offset mv_offset to the motionvector mvL1R1_B1 of the prediction of the direction L1 to an additionalcandidate motion vector of the direction L1.

When a motion vector List0MV of the direction L0, which is obtained froman available adjacent prediction unit, has a value (mx0, my0), a motionvector List1 MV of the direction L1 has a value (mx1, my1), and areference picture of the direction L1 and a reference picture of thedirection L0 are positioned on corresponding locations with respect to acurrent picture, the additional candidate motion information generatingunit 1540 may add and subtract a predetermined offset to and from amotion vector of the prediction of the direction L0 and a motion vectorof the prediction of the direction L1 to generate additional candidatemotion information as follows.

List0MV=(mx0+offset, my0), List1 MV=(mx0+offset, my0);

List0MV=(mx0−offset, my0), List1 MV=(mx0−offset, my0);

List0MV=(mx0, my0+offset), List1 MV=(mx0, my0+offset);

List0MV=(mx0, my0−offset), List1 MV=(mx0, my0−offset);

List0MV=(mx0+offset, my0+offset), List1 MV=(mx0+offset, my0+offset);

List0MV=(mx0+offset, my0−offset), List1 MV=(mx0+offset, my0−offset);

List0MV=(mx0−offset, my0+offset), List1 MV=(mx0−offset, my0+offset); and

List0MV=(mx0−offset, my0−offset), List1MV=(mx0−offset, my0−offset)

According to another exemplary embodiment, the additional candidatemotion information generating unit 1540 may change available motioninformation of spatial prediction units and temporal prediction units togenerate additional candidate motion information. When available motioninformation of spatial prediction units and temporal prediction unitsincludes bi-directional motion vector information of the directions L0and L1, the additional candidate motion information generating unit 1540may add uni-directional information, which is generated by splitting theprediction of the directions L0 and L1, to additional candidate motioninformation. For example, it is assumed that bi-directional motioninformation obtained from available spatial prediction units andtemporal prediction units includes motion information of the directionL0, which includes a motion vector List0MV of the direction L0 and areference picture index List0REF indicating a reference picture of thedirection L0, and motion information of the direction L1, which includesa motion vector List1 MV of the direction L1 and a reference pictureindex List1 REF indicating a reference picture of the direction L1. Theadditional candidate motion information generating unit 1540 may dividethe bi-directional motion information to generate two pieces ofuni-directional motion information and add the two pieces ofuni-directional motion information to additional candidate motioninformation. That is, the additional candidate motion informationgenerating unit 1540 may divide the bi-directional motion informationinto uni-directional motion information of the direction L0 including {amotion vector List0MV of the direction L0 and a reference picture indexList0REF indicating a reference picture of the direction L0} anduni-directional motion information of the direction L1 including {amotion vector List1 MV of the direction L1 and a reference picture indexList1 REF indicating a reference picture of the direction L1} and mayadd the uni-directional motion information to additional candidatemotion information.

In addition, when available motion information of spatial predictionunits and temporal prediction units includes uni-directional motioninformation of the direction L0 and uni-directional motion informationof the direction L1, the additional candidate motion informationgenerating unit 1540 may add bi-directional motion information generatedby combining the uni-directional motion information of the directions L0and L1 to additional candidate motion information. For example, whenuni-directional motion information of the direction L0, {which includesa motion vector List0MV of the direction L0 and a reference pictureindex List0REF indicating a reference picture of the direction L0}, anduni-directional motion information of the direction L1, {which includesa motion vector List1 MV of the direction L1 and a reference pictureindex List1 REF indicating a reference picture of the direction L1}exist as motion information obtained from prediction units that arespatially and temporally collocated to a current prediction unit, theuni-directional motion information of the direction L0 and theuni-directional motion information of the direction L1 are combined togenerate bi-directional motion information and the generatedbi-directional motion information may be added to additional candidatemotion information.

In addition, the additional candidate motion information generating unit1540 may add a motion vector having a predetermined value and areference index to any one of the uni-directional motion information ofthe direction L0 and the uni-directional motion information of thedirection L1 to generate uni-directional motion information of differentdirections such that the obtained bi-directional motion information toadditional candidate motion information. For example, when onlyuni-directional motion information of the direction L0, {which includesa motion vector List0MV of the direction L0 and a reference pictureindex List0REF indicating a reference picture of the direction L0},exists as motion information obtained from prediction units that arespatially and temporally collocated to a current prediction unit, theadditional candidate motion information generating unit 1540 may set amotion vector having a predetermined value such as (0,0) as a motionvector List1 MV of the direction L1 and may set a reference pictureindex List1 REF indicating a reference picture of the direction L1 as apredetermined value 0 to generate motion information of the directionL1, and may combine the generated motion information of the direction L1and the existing motion information of the direction L0 such that thegenerated bi-directional motion information is included in additionalcandidate motion information.

The additional candidate motion information generating unit 1540 maygenerate only motion vector information from among motion information ofan available prediction unit by using an available prediction unit andmay separately set the remaining reference direction (predictiondirection) information or a reference picture index. In this case, whenthe additional candidate motion information generating unit 1540generates additional candidate motion information by using motioninformation of an available prediction unit, the additional candidatemotion information generating unit 1540 may generate reference directioninformation according to a slice type of a current prediction unit. Forexample, when a current prediction unit is included in a P slice, areference direction included in the additional candidate motioninformation is set as the direction L0. When a current prediction unitis included in a B slice, a reference direction may be set as abi-direction including prediction of the directions L0 and L1. Inaddition, the additional candidate motion information generating unit1540 may set a reference picture index within a range among (0˜thereference picture index of available prediction unit) and may add aplurality of reference picture indexes to additional candidate motioninformation.

When the additional candidate motion information generating unit 1540generates the reference picture index, the additional candidate motioninformation generating unit 1540 may use a reference picture indexindicating a reference picture having the highest frequency from amongreference pictures included in motion information of available spatialprediction units and temporal prediction units or may use a referencepicture index indicating a reference picture that is referred to by themost adjacent prediction units of a current prediction unit, instead ofsetting a reference picture index having a predetermined value, asdescribed above.

In addition, when the number of pieces of default candidate motioninformation generated by the spatial candidate motion informationgenerating unit 1510 and the temporal candidate motion informationgenerating unit 1520 is less than a predetermined number ‘n’, theadditional candidate motion information generating unit 1540 may omit aprocess for checking whether additional candidate motion informationincluded in candidate motion information is duplicated such that thetotal number of pieces of candidate motion information may be ‘n’. Thatis, the additional candidate motion information generating unit 1540 mayadd additional candidate motion information generated by changingdefault motion information to the candidate motion information eventhough the additional candidate motion information is the same asdefault motion information.

FIG. 22 is a flowchart of a method of encoding a motion vector,according to an exemplary embodiment.

Referring to FIG. 22, in operation 2310, the motion estimator 420performs motion prediction on a current prediction unit to obtain motioninformation about the current prediction unit.

In operation 2320, the candidate motion information generating unit 1410determines whether motion information of spatial prediction units thatare spatially collocated to a current prediction unit and motioninformation of temporal prediction units that are temporally collocatedto the current prediction unit are available. As described above, thecandidate motion information generating unit 1410 checks whether motioninformation of adjacent prediction units A0 and A1 positioned on theleft of the current prediction unit and motion information of adjacentprediction units B0, B1, and B2 positioned above the current predictionunit are available and may add motion information of an availableadjacent prediction unit to default candidate motion information. Inaddition, the candidate motion information generating unit 1410 checkswhether motion information of prediction units of a predeterminedlocation from among prediction units of a previous picture is availableand may add the motion information of the previous picture to thedefault candidate motion information.

In operation 2330, when the number of pieces of motion information ofspatial prediction units and temporal prediction units is less than apredetermined number ‘n’, the candidate motion information generatingunit 1410 may generate additional candidate motion information by usingmotion information of available spatial prediction units and temporalprediction units such that the total number of pieces of candidatemotion information may be ‘n’.

In operation 2340, the motion information encoder 1420 encodes motioninformation of the current prediction unit by using n pieces of motioninformation. In detail, the motion information encoder 1420 determinesmost similar motion information to motion information of a currentprediction unit from among the generated candidate motion informationand transmits index information indicating the determined motioninformation. For example, when motion information is a motion vector,the candidate motion information generating unit 1410 generatesprediction motion vector candidates of the current prediction unit andthe motion information encoder 1420 may encode information about anindex value indicating a most similar prediction motion vector to themotion vector of the current prediction unit from among predictionmotion vector candidates and information about a difference valuebetween the motion vector of the current prediction unit and theprediction motion vector.

FIG. 23 is a block diagram of a motion vector decoding apparatus 2400according to an exemplary embodiment.

Referring to FIG. 23, the motion vector decoding apparatus 2400 includesan entropy decoder 2410, a motion information decoder 2420, and acandidate motion information generating unit 2430, i.e. a candidatemotion information generator.

The entropy decoder 2410 extracts motion information used in a currentprediction unit from among candidate motion information from abitstream. For example, when motion information is a motion vector, theentropy decoder 2410 extracts an index indicating motion informationabout a prediction motion vector index, a difference value between theprediction motion vector and an original motion vector, referencepicture information, and prediction direction information.

Like the candidate motion information generating unit 1410 shown in FIG.14A, the candidate motion information generating unit 2430 obtainscandidate motion information by using motion information of adjacentprediction units that are temporally and spatially collocated to acurrent prediction unit, and generates additional candidate motioninformation by using motion information of prediction units that arespatially and temporally collocated to the current prediction unit suchthat the number of pieces of the candidate motion information is ‘n’.

The motion information decoder 2420 obtains a single piece of candidatemotion information generated by the candidate motion informationgenerating unit 2430 by using an index indicating motion information ofa current prediction unit obtained from a bitstream. As described above,when motion information is a motion vector, the motion informationdecoder 2420 obtains a single prediction motion vector from amongprediction motion vector candidates by using an index indicating theprediction motion vector obtained from a bitstream, extracts informationabout a difference value between the prediction motion vector and anoriginal motion vector from a bitstream, and then adds the differencevalue and the prediction motion vector to restore a motion vector of thecurrent prediction unit.

FIG. 24 is a flowchart of a method of decoding motion information,according to an exemplary embodiment.

Referring to FIG. 24, in operation 2510, the candidate motioninformation generating unit 2430 determines whether motion informationof spatial prediction units that are spatially collocated to a currentprediction unit and motion information of temporal prediction units thatare temporally collocated to the current prediction unit are available.In operation 2520, as the determination result, when the number ofpieces of available motion information of the spatial prediction unitsand temporal prediction units is less than a predetermined number ‘n’(where n is an integer), the candidate motion information generatingunit 2430 generates additional candidate motion information by usingavailable motion information of spatial prediction units and temporalprediction units such that the total number of pieces of candidatemotion information may be ‘n’.

In operation 2530, the entropy decoder 2410 obtains and outputs indexinformation indicating a motion information from among ‘n’ pieces ofcandidate motion information from a bitstream. In operation 2540, themotion information decoder 2420 obtains motion information of a currentprediction unit by using the motion information indicated by the index.As described above, when motion information is a motion vector, themotion information decoder 2420 obtains a single prediction motionvector from among prediction motion vector candidates by using the indexindicating the prediction motion vector obtained from a bitstream,extracts information about a difference value between the predictionmotion vector and an original motion vector from a bitstream, and thenadds the difference value and the prediction motion vector to restore amotion vector of the current prediction unit.

Exemplary embodiments can be written as computer programs and can beimplemented in general-use digital computers that execute the programsusing a computer readable recording medium. Examples of the computerreadable recording medium include magnetic storage media (e.g., ROM,floppy disks, hard disks, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs).

While several exemplary embodiments have been particularly shown anddescribed, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the present invention as definedby the following claims.

What is claimed is:
 1. A method of decoding an image, the methodcomprising: obtaining, by a decoder comprising a processor, a predictionmode of a current block, from a bitstream; when the prediction mode ofthe current block is inter-prediction, obtaining a spatial motion vectorpredictor candidate of the current block by using a motion vector of anavailable spatial block spatially related to the current block;obtaining a temporal motion vector predictor candidate of the currentblock by using motion vector of an available temporal block temporallyrelated to the current block; adding, when a number of the spatialmotion vector predictor candidate and the temporal motion vectorpredictor candidate is smaller than a predetermined number n, where n isan integer equal to two or greater, a zero vector to be a motion vectorpredictor candidate so that a number of the motion vector predictorcandidates is to be the predetermined number n; and obtaining a motionvector predictor of the current block based on information indicating amotion vector predictor among the motion vector predictor candidates,wherein the spatial motion vector predictor candidate is obtained fromneighboring blocks including a lower left block located on a lower leftside of the current block.